Motion capture systems obtain data regarding the location and movement of a human or other subject in a physical space, and can use the data as an input to an application in a computing system. Many applications are possible, such as for military, entertainment, sports and medical purposes. For instance, the motion of humans can be mapped to a three-dimensional (3-D) human skeletal model and used to create an animated character or avatar. Optical systems, including those using visible and invisible, e.g., infrared, light, use cameras to detect the presence of a human in a field of view. However, further refinements are needed which allow a human to interact more naturally with an application.